I'm trying to login to my 365 subscription on my Mac

Update the Office apps using the same source from which they were installed; Microsoft documents “Unknown Error 0x0” as a resolved Office for Mac licensing issue whose fix is delivered through current app updates.^1^

1. Check the macOS version first

Select Apple menu → About This Mac.

• macOS 12 or later: continue with the update steps below.
• Earlier than macOS 12: the update-based 0x0 fix is unavailable on that operating system. Upgrade macOS if the Mac supports it, or use Microsoft 365 on the web or another supported device as the immediate alternative.^2^

2. Install the licensing fix

First close Word, Excel, Outlook, PowerPoint, OneNote, and any other Office apps.

If Office was downloaded from Microsoft:

1. Open Finder → Applications → Microsoft AutoUpdate.
2. If it is absent there, open Finder and browse to: /Library/Application Support/Microsoft/MAU2.0/
3. Select Update All.
4. When all updates finish, open Word or Excel and sign in again.

If the apps were installed from Apple’s Mac App Store:

1. Open App Store → Updates.
2. Update Word, Excel, PowerPoint, Outlook, and OneNote, or select Update All.
3. Reopen an Office app and try activation again.

Do not mix the two update methods; use the one matching the installation source.^1^

3. Verify the licensed account

The subscription being paid does not necessarily mean the desktop app is signing in with the licensed account.

1. Visit https://account.microsoft.com/services.
2. Sign in with the account being used in Office.
3. Select Install Microsoft 365 or Office and confirm that the license appears.
4. In Word or Excel, sign out and choose Sign in with another account if Office currently shows a different address.

For a business subscription issued by an organization, ask its Microsoft 365 administrator to confirm that the license is assigned to this exact work account.^3^

4. If 0x0 remains, reset the local Office licenses

The License Removal Tool removes all Office licenses stored on this Mac, so have the correct licensed account and password available before proceeding.

1. Close every Office application.
2. Open Microsoft’s license-removal instructions and download the tool from that page.^4^
3. Open the downloaded .pkg, select Continue, and follow the prompts. A local Mac administrator password may be required.
4. When the tool reports that the licenses were removed, select Close.
5. Open Word or Excel and sign in with the account confirmed in step 3.
6. Restart the Mac after activation succeeds.

If macOS reports an unidentified developer, do not routinely bypass the warning. Confirm that the package was downloaded directly through the Microsoft Support page and is signed by Microsoft; otherwise, delete it and download it again from that page.

If updating and resetting the license still fail, record the macOS version, Office version, installation source, and complete error text before contacting Microsoft 365 support or the organization’s administrator.

References

1. Unknown Error 0x0 or License not found error in Microsoft 365 or Office running on macOS | Microsoft Support
2. I cannot get Microsoft 365 working on my MacBook - Microsoft Q&A
3. [Activation](https://support.microsoft.com/microsoft-365-activation-licensing/what-to-try-if-you-can-t-install-or-activate-office-for-mac)
4. How to remove Office license files on a Mac